Originally Posted by Bus ted1
I agree with PNW Steve about the 5.9. Not all are governed at 55, as mine was set at 65. Also because of the use of this engine in Dodge Trucks there is all sorts of aftermarket support for these engines. It is very easy to raise the power levels substantially on the 12 valve and early 24 valves up to about 2003. After 2003 or so the engines are totally controlled by proprietary computer software and the only method outside factory help is to swap to a early manual fuel control. Easily done. The governed RPM and thus speed is very easily changed.
while power-adding can be a bit of its own slippery slope.. RPM raising can be an even more slippery slope.. while most of our bus engines may be able to spin faster than they do, doing so is often out of their optimum power band so you actually Lose power not gain it.. though you can gain a few MPH on top end just from too low of final drive ratio...
one of the things to think about is you are taking an engine that has for many years spun at its current top end RPM as the max.. over the years it will have most likely developed a "ring ridge" in the cylinders.. at the spot where the piston travelled the highest..
when you spin an engine up.. the weight of the piston can actually "stretch" the rod slightly and temporarily.. metal reacts to the forces applied and may flex..
for 150k or whatever miles it never spun over that top RPM.. the rod never will have stretched further.
now ad some RPM.. and suddenly your rod stretch is a little greater.. now you are attempting to run the piston up on said ridge... the rings are going to flex .. piston may stop a little faster than it did.. bearings may run in a slightly different position than they did previously etc..
all this sounds minuscule.. but could possibly shorten the life of said engine.. on a fresh rebuild, its much safer to turn up the RPM as all of the parts are fresh and will be broken in with the common Max RPM..
Upping the power is just as slippery of slope.. you can have bearings or other parts which could be weak.. however handled the oriignal power rating.. then you turn it up.. and thuings may wear out quicker or break..
the other thung is to make sure on these engines which were shared amongst Medium duty trucks and pickup trucks to make sure the hardware matches what you want to do... is the 5.9 that you want to make more power and spin faster (because joey down the street did it in his Dodge).. the same engine? or does it differ..